A CMOS (complementary metal oxide semiconductor) image sensor is a device employing a switching method where outputs of unit pixels are sequentially detected by MOS transistors, the number of which is identical to that of unit pixels. The MOS transistors are formed on a semiconductor substrate, and a control circuit and a signal processing circuit are used as peripheral circuits.
That is, a photodiode and a MOS transistor are formed in each unit pixel so that the CMOS image sensor realizes an image by sequentially detecting electric signals of the unit pixels using the switching method. Since the CMOS image sensor uses CMOS fabrication technology, the power consumption is low and the fabrication process is simplified. This simplification can be due to the reduced number of photo processes.
In order to increase the photo sensitivity of the CMOS image sensor, a microlens is formed above the photodiode to refract the path of incident light, making it possible to concentrate an increased amount of light on the photodiode area.
However, the light incident on the edge of the microlens is not incident in parallel with an optical axis, but may be incident in an off-axis form.
Accordingly, the light, which is not parallel with the optical axis, is refracted from the microlens to reach an undesirable area in the substrate, for example, a wiring area, through the path. Therefore, the path taken to the undesirable area creates a problem by not focusing the light on a light reaction area such that shifting of the focus occurs, thereby causing a malfunction of the device.